This invention relates to the next evolution of IC cards wherein an RF downlink communication capability is incorporated into the IC card so that noncontact remote interrogation of the IC card is permitted.
The backbone of credit card communication is the magnetic stripe which is scanned by appropriate readers within remote terminals for the verification of transactions or the delivery of cash. The advantage of the magnetic stripe is that it is an entirely passive device with a non-volatile memory. The disadvantages are that it requires manual insertion into a reading device and that the amount of static information which can be stored is limited. One obvious way to limit credit card fraud is to increase the amount of personal data such as fingerprints and portraits contained within each credit card; this, however, is far beyond the capabilities of the magnetic stripe.
The requirement for increased data capability implies the need for a smart-card or integrated circuit (IC) card with its attendant memory capability. However, the Credit Card Industry has been slow to adopt IC cards due to their inherent problems. Such cards are often unreliable, due largely to the need for metallic contacts to couple the card to a card reader. The contacts are readily tarnished, have a short useful life and require a precision card reading mechanism.
A solution to this problem is proposed in U.S. Pat. Nos. 4,701,601 (Francini) and 4,791,283 (Burkhardt) wherein the identification data is transfered from the IC card by using magnetic stripe emulators. This prior art increases the storage capability of the credit card, but does not improve the communication of the credit card with the terminal. Other solutions involving communication via magnetic induction are proposed in U.S. Pat. Nos. 4,650,981 (Foletta) and 4,960,983 (Takesi).
Another example of an IC card transaction device is shown in U.S. Pat. No. 4,575,621 (Dreifus), which uses optical coupling for communication. All these proposals require manual insertion of a IC card into a terminal, which limits their application.
IC cards have been evolving in a manner similar to telephone technology and are utilizing wireless Radio Frequency for communication rather than magnetic stripes, metallic contacts or magnetic induction. A recent example of this technology is disclosed in U.S. Pat. No. 5,212,373 (Shuzo Fujioka, et al) which defines a noncontact IC card employing an RF interface.
These approaches require a battery powered credit card which diminishes its utility. Credit cards and other identification cards need to be totally passive which is why they are so useful, whereas IC cards are usually battery powered. To solve the power problem, some passive transponders, for example, have been used in various automatic identification schemes for vehicles such as automobiles and railroad cars. These have applications for monitoring the location of freight cars and the automatic collection of toll fees for vehicular traffic on a nonintrusive basis.
The key to this technology is passive responders deriving their energy from external sources. These sources are either the motion of a conductor through a magnetic field for moving traffic or a conductor in an oscillating magnetic field for stationary traffic. Examples of this application are disclosed in U.S. Pat. Nos. 3,090,042 (Kleist) and 4,912,471 (Tyburski).
These approaches to energizing passive responders have serious shortcomings when applied to electronics embedded in small plastic cards as exemplified by credit cards, driver licences, identification badges and IC cards in general. The size of the conductors is constrained by the size of the plastic card which in turn limits the induced voltages and therefore the power to drive the responder. In these cases, a more directed form of energy is required for passive responders on a smart card and this can be provided by a directed beam of radiant energy onto a large array of photovoltaic cells covering the card. For nonintrusive interrogation, especially at night, infrared illumination may be used. U.S. Pat. No. 4,575,621 (Dreifus) uses optical coupling for both communication and energy transfer to a portable electronic transaction device to avoid mechanical contact problems. But this is performed within the confines of a terminal slot and does not permit remote interrogation. Furthermore, the portable electronic transaction device contains a battery which limits the usefulness of the disclosure since credit cards should, of necessity, be totally passive. In U.S. Pat. No. 4,916,296, which is conceptually similar to Dreifus' disclosure, Streck advocates the use of solar cells to provide energy, but confines his disclosure to optical(infra-red) communication which appears simpler than RF communication. However, simple on-card RF communication is possible by using Dielectric Resonant Oscillators (DRO) which are based on the instability of some transistor amplifier configurations.
An excellent introduction to this subject is Boyles' paper on the oscillator as a reflection amplifier in which the transistor has a negative resistance, sustains the reflections, and defines explicit criteria for oscillations to occur. Following this, the paper by Wilson and others gives a useful design procedure for DROs employing Field Effect Transistors (FET). However, the most important aid in the design of DROs is the authoritative work by Gonzalez on Microwave Transistor Amplifiers.
Remarkably, this is fertile field for patents as exemplified by U.S. Pat. No. 4,149,127 for an early dielectric resonator stabilized microstrip oscillator and U.S. Pat. No. 4,707,669 for a dielectric resonator microwave oscillator whose circuit parameters are optimized to give enhanced negative resistance. More recently, U.S. Pat. No. 5,180,966 defines a DRO having an improved output filter and U.S. Pat. No. 5,187,451 minimizes the microstrip width and length for a specific DRO.
By using a DRO based on microstrip technology and utilizing a single FET, a simple on-card RF system is defined that employs Frequency Shift Keying (FSK) to modulate the carrier and transmit the identification data. This is based on the fact that the frequency of oscillation is inversely proportional to the gate-to-source capacitance. Since this capacitance varies with the gate-to-source bias, it provides a simple mechanism for modulating the carrier. By coupling this bias to the data stream, an FSK modulation system is achieved.
With regard to terminals to support the RF interface, many electronic companies have developed systems that enable the wireless transmission of digital data from computer to computer to be performed. Specifically, these systems are for small offices to avoid wiring problems. These systems with minor modifications to the carrier frequency, signal modulation data format and the addition of a radiant energy source, can serve as the interrogation terminals and can be specifically tailored to applications such as automatic teller support, traffic monitoring, or general identification and surveillance services.
An array of photovoltaic cells is an obvious way to provide sufficient energy to power a passive device. Furthermore, directed beams of radiant energy serve as the interrogation query of the IC card, or equivalently the communication uplink. This mode of informationless uplink is possible, because once the IC card is energized the identification data can be automatically transmitted over the IC card's RF downlink without any need to turn the IC card on or off. Also, the radiant energy uplink and the RF downlink do not have to be performed within the confines of some reader apparatus. This means that remote interrogation of the IC card can be performed opening up a whole spectrum of applications for the IC card beyond banking transactions, ranging from traffic monitoring to passport control, data entry and areas of surveillance.